Method of controlling ammonia amount adsorbed in selective catalytic reduction catalyst and exhaust system using the same

ABSTRACT

A method of controlling ammonia amount adsorbed in a selective catalytic reduction (SCR) catalyst, may include detecting current temperature of the SCR catalyst, reading predicted maximum temperature of the SCR catalyst after a predetermined time based on the current temperature of the SCR catalyst, determining a target adsorption amount of ammonia (NH3) based on the predicted maximum temperature of the SCR catalyst, and controlling amount of urea or the NH3 injected into exhaust gas based on the target adsorption amount of the NH3 and current adsorption amount of the NH3.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of Korean Patent Application No. 10-2013-0161441 filed on Dec. 23, 2013, the entire contents of which is incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst and an exhaust system using the same. More particularly, the present invention relates to a method of controlling ammonia amount adsorbed in a selective catalytic reduction (SCR) catalyst and an exhaust system using the same that improves performance of the SCR catalyst by adsorbing more ammonia (NH3) in the SCR catalyst while preventing slip of the NH3 from the SCR catalyst.

2. Description of Related Art

Generally, exhaust gas flowing out from an engine through an exhaust manifold is urged into a catalytic converter mounted at an exhaust pipe and is purified therein. After that, the noise of the exhaust gas is decreased while passing through a muffler and the exhaust gas is then emitted into the air through a tail pipe. The catalytic converter purifies pollutants contained in the exhaust gas. In addition, a particulate filter for trapping particulate matter (PM) contained in the exhaust gas is mounted in the exhaust pipe.

A selective catalytic reduction (SCR) catalyst is one type of such a catalytic converter.

Reducing agent such as urea, ammonia, carbon monoxide and hydrocarbon (HC) reacts better with nitrogen oxide than with oxygen in the SCR catalyst.

An exhaust system of a vehicle provided with the SCR catalyst includes a urea tank and dosing module. The dosing module injects reducing agent such as urea into the exhaust gas passing through the exhaust pipe, and thereby the SCR catalyst purifies the nitrogen oxide efficiently.

The reducing agent injected from the dosing module is adsorbed in the SCR catalyst, is released if the exhaust gas containing the nitrogen oxide passes through the SCR catalyst, and reacts with the nitrogen oxide.

However, amount of the reducing agent adsorbed in the SCR catalyst is closely related to temperature of the SCR catalyst. Therefore, if the amount of the reducing agent more than maximum amount of the reducing agent that can be adsorbed in current temperature of the SCR catalyst is adsorbed in the SCR catalyst, a portion of the reducing agent is slipped from the SCR catalyst.

Ammonia is typically used as the reducing agent of the SCR catalyst. If the ammonia is slipped from the SCR catalyst, the slipped ammonia may cause stink and customers may have complaints. Therefore, it is very important to prevent the reducing agent from being slipped from the SCR catalyst.

According to a conventional method of controlling NH3 amount adsorbed in the SCR catalyst, the SCR catalyst is controlled to adsorb NH3 amount obtained by dividing maximum NH3 amount at the current temperature of the SCR catalyst by a substantially large safety factor. That is, the SCR catalyst is controlled to absorb the NH3 amount that is smaller than the maximum NH3 amount to prevent slip of the NH3 from the SCR catalyst. Therefore, the SCR catalyst may underperform.

In addition, since the SCR catalyst underperforms, volume of the SCR catalyst should be increased.

The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst and an exhaust system using the same having advantages of improving performance of the SCR catalyst and reducing volume of the SCR catalyst by adsorbing more NH3 in the SCR catalyst while preventing slip of the NH3 from the SCR catalyst.

In an aspect of the present invention, a method of controlling ammonia amount adsorbed in a selective catalytic reduction (SCR) catalyst, may include detecting current temperature of the SCR catalyst, reading predicted maximum temperature of the SCR catalyst after a predetermined time based on the current temperature of the SCR catalyst, determining a target adsorption amount of ammonia (NH3) based on the predicted maximum temperature of the SCR catalyst, and controlling amount of urea or the NH3 injected into exhaust gas based on the target adsorption amount of the NH3 and current adsorption amount of the NH3.

The target adsorption amount of the NH3 is a maximum NH3 amount that is adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.

The target adsorption amount of the NH3 is a value obtained by multiplying a predetermined safety factor to a maximum NH3 amount that is adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.

The reading of the predicted maximum temperature of the SCR catalyst after the predetermined time is performed when the current temperature of the SCR catalyst is higher than or equal to urea conversion temperature.

The predicted maximum temperature of the SCR catalyst after the predetermined time according to the current temperature of the SCR catalyst is stored in a predetermined map.

The predetermined map is stored in a non-volatile memory of a vehicle.

The method may further include detecting actual maximum temperature of the SCR catalyst for the predetermined time, determining whether the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time, and storing the actual maximum temperature of the SCR catalyst for the predetermined time as the predicted maximum temperature of the SCR catalyst after the predetermined time in the predetermined map when the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time.

In another aspect of the present invention, an exhaust system may include an engine generating driving torque by burning mixture of air and fuel and exhausting exhaust gas generated at combustion process through an exhaust pipe, a reducing agent supplier mounted on the exhaust pipe downstream of the engine and adapted to inject urea or ammonia (NH3) into the exhaust gas, wherein the urea is decomposed into the ammonia, a selective catalytic reduction (SCR) catalyst mounted on the exhaust pipe downstream of the reducing agent supplier and adapted to absorb the ammonia and to reduce nitrogen oxide contained in the exhaust gas using adsorbed, injected or decomposed ammonia, a temperature sensor detecting temperature of the SCR catalyst, and a controller reading predicted maximum temperature of the SCR catalyst based on current temperature of the SCR catalyst after a predetermined time, determining a target adsorption amount of the ammonia based on the predicted maximum temperature of the SCR catalyst, and controlling amount of the urea or the NH3 injected from the reducing agent supplier based on the target adsorption amount of the NH3 and current adsorption amount of the NH3.

The target adsorption amount of the NH3 is maximum NH3 amount adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.

The target adsorption amount of the NH3 is a value obtained by multiplying a predetermined safety factor to a maximum NH3 amount adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.

The controller reads the predicted maximum temperature of the SCR catalyst after the predetermined time only when the current temperature of the SCR catalyst is higher than or equal to urea conversion temperature.

The predicted maximum temperature of the SCR catalyst after the predetermined time according to the current temperature of the SCR catalyst is stored in a predetermined map.

The predetermined map is stored in a non-volatile memory of a vehicle.

The controller stores an actual maximum temperature of the SCR catalyst for the predetermined time as the predicted maximum temperature of the SCR catalyst after the predetermined time in the predetermined map when the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time.

The methods and apparatuses of the present invention have other features and advantages which will be apparent from or are set forth in more detail in the accompanying drawings, which are incorporated herein, and the following Detailed Description, which together serve to explain certain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an exhaust system according to an exemplary embodiment of the present invention.

FIG. 2 is a block diagram of an exhaust system executing a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to an exemplary embodiment of the present invention.

FIG. 3 is a flowchart of a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to an exemplary embodiment of the present invention.

FIG. 4 is a graph illustrating one example of temperature of a selective catalytic reduction catalyst to a time.

FIG. 5 shows one example of a predetermined map.

FIG. 6 is a graph illustrating target adsorption amount of ammonia according to a conventional method and target adsorption amount of ammonia according to the present exemplary embodiment.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various features illustrative of the basic principles of the invention. The specific design features of the present invention as disclosed herein, including, for example, specific dimensions, orientations, locations, and shapes will be determined in part by the particular intended application and use environment.

In the figures, reference numbers refer to the same or equivalent parts of the present invention throughout the several figures of the drawing.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of the present invention(s), examples of which are illustrated in the accompanying drawings and described below. While the invention(s) will be described in conjunction with exemplary embodiments, it will be understood that the present description is not intended to limit the invention(s) to those exemplary embodiments. On the contrary, the invention(s) is/are intended to cover not only the exemplary embodiments, but also various alternatives, modifications, equivalents and other embodiments, which may be included within the spirit and scope of the invention as defined by the appended claims.

An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an exhaust system according to an exemplary embodiment of the present invention.

As shown in FIG. 1, nitrogen oxide in exhaust gas is removed while the exhaust gas generated in an engine 10 passes through a selective catalytic reduction (SCR) catalyst 30. If necessary, a particulate filter for trapping particulate matter contained in the exhaust gas and/or an oxidation catalyst for oxidizing carbon monoxide or hydrocarbon contained in the exhaust gas may be used. The exhaust system illustrated in FIG. 1 shows a simplified layout of an exhaust system to which spirit of the present invention can be applied, and it is to be understood that a range of the present invention is not limited to the exhaust system illustrated in FIG. 1.

The engine 10 burns air/fuel mixture in which fuel and air are mixed to convert chemical energy into mechanical energy. The engine 10 is connected to an intake manifold 16 to receive the air into a combustion chamber 12, and is connected to an exhaust manifold 18 such that the exhaust gas generated in combustion process is gathered in the exhaust manifold 18 and is exhausted to the exterior. An injector 14 is mounted in the combustion chamber 12 to inject the fuel into the combustion chamber 12.

An exhaust pipe 20 is connected to the exhaust manifold 18 and is adapted to discharge the exhaust gas to the exterior of a vehicle.

The SCR catalyst 30 is mounted on the exhaust pipe 20 and is adapted to reduce the nitrogen oxide contained in the exhaust gas into nitrogen gas using reducing agent.

For these purposes, the exhaust system further includes a urea tank, a urea pump and a dosing module 34. For brief description, the urea tank and the urea pump are not illustrated in the drawings. In addition, urea is injected by the dosing module 34 in this specification but it is not limited that the dosing module 34 just injects the urea. That is, the dosing module 34 may inject ammonia. Furthermore, reducing agent other than the ammonia can be injected together with the ammonia or by itself.

The dosing module 34 injects the urea pumped by the urea pump into the exhaust pipe 20. The dosing module 34 is mounted on the exhaust pipe 20 between the engine 10 and the SCR catalyst 30 and injects the urea into the exhaust gas before entering the SCR catalyst 30. The urea injected into the exhaust gas is decomposed into the ammonia and the decomposed ammonia is used as the reducing agent for the nitrogen oxide.

Meanwhile, the urea tank, the urea pump and the dosing module described in this specification are examples of reducing agent suppliers, and it is to be understood that a range of the present invention is not limited to the examples of the reducing agent suppliers. That is, other types of the reducing agent suppliers can be used in an exemplary embodiment of the present invention.

The exhaust system further includes a plurality of sensors including a first NOx sensor 32, a temperature sensor 36 and second NOx sensor 38.

The first NOx sensor 32 is mounted on the exhaust pipe 20 upstream of the SCR catalyst 30 and detects NOx amount contained in the exhaust gas at an upstream of the SCR catalyst.

The temperature sensor 36 is mounted on the exhaust pipe 20 upstream of the SCR catalyst 30 or in the SCR catalyst 30, and detects the temperature of the exhaust gas at the upstream of the SCR catalyst 30 or in the SCR catalyst 30. For better comprehension and ease of description, the temperature of the SCR catalyst 30 described in this specification and claim may be temperature of the exhaust gas at the upstream of the SCR catalyst 30 or temperature of the exhaust gas in the SCR catalyst 30.

The second NOx sensor 38 is mounted on the exhaust pipe 20 downstream of the SCR catalyst 30 and detects the NOx amount contained in the exhaust gas at a downstream of the SCR catalyst 30. In various exemplary embodiments, the NOx amount at the upstream of the SCR catalyst 30 may be predicted based on exhaust flow rate, operation history of the engine, temperature of the SCR catalyst 30, injection amount of the reducing agent and/or amount of the reducing agent absorbed in the SCR catalyst 30, instead of using the second NOx sensor 38.

The exhaust system further includes a controller 40. The controller 40 controls operation of the injector 14 and the dosing module 34 based on the detection of the first and second NOx sensors 32 and 38 and the temperature sensor 36.

FIG. 2 is a block diagram of an exhaust system executing a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to an exemplary embodiment of the present invention.

The temperature sensor 36 detects the temperature of the SCR catalyst 30 and transmits a signal corresponding thereto to the controller 40.

The first NOx sensor 32 detects the NOx amount contained in the exhaust gas at the upstream of the SCR catalyst 30 and transmits a signal corresponding thereto to the controller 40.

The second NOx sensor 38 detects the NOx amount contained in the exhaust gas at the downstream of the SCR catalyst 30 and transmits a signal corresponding thereto to the controller 40.

The controller 40 calculates target adsorption amount of the NH3 that will be adsorbed in the SCR catalyst 30 based on the temperature of the SCR catalyst 30 detected by the temperature sensor 36, and controls the urea amount that is injected by the dosing module 34 based on the target adsorption amount of the NH3 and the NOx amount contained in the exhaust gas at the upstream of the SCR catalyst 30 that is detected by the first NOx sensor 32.

In addition, the controller 40 may evaluate performance of the SCR catalyst 30 based on the NOx contained in the exhaust gas at the downstream of the SCR catalyst 30 that is detected by the second NOx sensor 38.

Furthermore, the controller 40 may control fuel amount that is injected by the injector 14 and injection timing based on driving conditions of the vehicle.

The controller 40 can be realized by one or more processors activated by a predetermined program, and the predetermined program can be programmed to perform each step of a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to exemplary embodiments of the present invention.

Meanwhile, the controller 40 may include a memory 42. It is exemplified in this specification but is not limited that the memory 42 is provided in the controller 40. The memory 42 may be a non-volatile memory.

FIG. 3 is a flowchart of a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to an exemplary embodiment of the present invention, FIG. 4 is a graph illustrating one example of temperature of a selective catalytic reduction catalyst to a time, and FIG. 5 shows one example of a predetermined map.

As shown in FIG. 3, a method of controlling ammonia amount adsorbed in a selective catalytic reduction catalyst according to an exemplary embodiment of the present invention begins when an ignition key is switched on at step S100.

If the ignition key is switched on at the step S100, the temperature sensor 36 detects the current temperature of the SCR catalyst 30 at step S110 and transmits the signal corresponding thereto to the controller 40.

If the controller 40 receives the signal corresponding to the current temperature of the SCR catalyst 30, the controller 40 determines whether the current temperature of the SCR catalyst 30 is higher than or equal to urea conversion temperature at step S120. Herein, the urea conversion temperature is temperature where the urea injected by the dosing module 34 can be decomposed into the ammonia and the decomposed ammonia can be adsorbed in the SCR catalyst 30. If the urea is injected at temperature lower than the urea conversion temperature, the urea cannot be decomposed into the ammonia nor cannot be adsorbed in the SCR catalyst 30 and be slipped from the SCR catalyst 30 if being decomposed. Therefore, the method according to an exemplary embodiment of the present invention can be operated normally at a temperature higher than or equal to the urea conversion temperature.

If the current temperature of the SCR catalyst 30 is lower than the urea conversion temperature at the step S120, the method returns to the step S100. If the current temperature of the SCR catalyst 30 is higher than or equal to the urea conversion temperature at the step S120, the controller 40 reads predicted maximum temperature of the SCR catalyst 30 after predetermined time t based on the current temperature of the SCR catalyst 30 at step S130. As shown in FIG. 5, the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t according to the current temperature of the SCR catalyst 30 is stormed in a predetermined map, and the predetermined map may be stored in the memory 42. Since the memory 42 is the non-volatile memory, the predetermined map is not erased from the memory 42.

Although the temperature of the SCR catalyst 30 changes continuously, the temperature of the SCR catalyst 30 can change within a specific range. That is, the temperature of the SCR catalyst 30 can be equal to or lower than the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t. In addition, if the temperature of the SCR catalyst 30 changes to temperature higher than the predicted maximum temperature of the SCR catalyst 30 for the predetermined time t, the highest temperature is stored as the predicted maximum temperature of the SCR catalyst 30 in the predetermined map.

If the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t according to the current temperature of the SCR catalyst 30 is read at the step S130, the controller 40 calculates target adsorption amount of the NH3 based on the predicted maximum temperature at step S140. As described above, since the temperature of the SCR catalyst 30 can change to the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t at the highest, the NH3 cannot be slipped from the SCR catalyst 30 if the target adsorption amount of the NH3 is calculated based on the predicted maximum temperature. In various exemplary embodiments, the target adsorption amount of the NH3 may be maximum NH3 amount that the SCR catalyst 30 can absorb at the predicted maximum temperature of the SCR catalyst 30. In various exemplary embodiments, the target adsorption amount of the NH3 may be a value obtained by multiplying a predetermined safety factor to the maximum NH3 amount that the SCR catalyst 30 can absorb at the predicted maximum temperature of the SCR catalyst 30. In this case, the safety factor may be a value close to 1 (e.g., 1.1 or 1.2).

If the target adsorption amount of the NH3 is calculated at the step S140, the controller 40 controls the urea amount injected into the exhaust gas by the dosing module 34 based on the target adsorption amount of the NH3 and current NH3 amount adsorbed in the SCR catalyst 30 at step S150. Additionally, the NOx amount contained in the exhaust gas at the upstream of the SCR catalyst 30 may be considered.

After that, the temperature sensor 36 detects actual maximum temperature of the SCR catalyst 30 for the predetermined time t at step S160 and transmits the signal corresponding thereto to the controller 40. The step S160 is performed to update the predetermined map, and the process will be described in detail with reference to FIG. 4 and FIG. 5.

If the actual maximum temperature of the SCR catalyst 30 for the predetermined time t is detected at the step S160, the controller 40 determines whether the actual maximum temperature of the SCR catalyst 30 for the predetermined time t is higher than the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t at step S170.

If the actual maximum temperature of the SCR catalyst 30 for the predetermined time t is lower than or equal to the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t at the step S170, the method returns to the step S100. If when the actual maximum temperature of the SCR catalyst 30 for the predetermined time t is higher than the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t at the step S170, the controller 40 updates the predetermined map at step S180. The update of the predetermined map will be described in detail.

As shown in FIG. 4, the temperature of the SCR catalyst 30 changes continuously as time goes by. If the current temperature of the SCR catalyst 30 is Tc, the predicted maximum temperature of the SCR catalyst 30 after the predetermined time t is firstly set to T1 (please refer to lower graph in FIG. 5). After that, the temperature of the SCR catalyst 30 rises to T2 for the predetermined time t when the current temperature of the SCR catalyst 30 is Tc. In this case, the predicted maximum temperature of the SCR catalyst 30 is reset to T2 (please refer to upper graph in FIG. 5). If the temperature of the SCR catalyst 30 does not rise to T1 for the predetermined time t when the current temperature of the SCR catalyst 30 is Tc, the predicted maximum temperature of the SCR catalyst 30 is maintained to T1. The predetermined map is continuously updated in such ways.

FIG. 6 is a graph illustrating target adsorption amount of ammonia according to a conventional method and target adsorption amount of ammonia according to the present exemplary embodiment. A solid line indicates the target adsorption amount of the NH3 according to an exemplary embodiment of the present invention and a dotted line indicates the target adsorption amount of the NH3 according to a conventional method in FIG. 6.

As shown in FIG. 6, the target adsorption amount of the NH3 at the current temperature Tc of the SCR catalyst 30 is m1 according to a conventional method, but the target adsorption amount of the NH3 at the current temperature Tc of the SCR catalyst 30 is m2 according to an exemplary embodiment of the present invention. In addition, the solid line indicating the target adsorption amount of the NH3 according to an exemplary embodiment of the present invention is positioned higher than the dotted line indicating the target adsorption amount of the NH3 according to a conventional method. That is, compared with a conventional method, the SCR catalyst 30 can absorb more NH3 at the same temperature of the SCR catalyst 30 according to an exemplary embodiment of the present invention. Therefore, full performance of the SCR catalyst 30 may be utilized and volume of the SCR catalyst 30 may be reduced.

As described above, an exemplary embodiment of the present invention may improve performance of the selective catalytic reduction catalyst and reduce volume of the selective catalytic reduction catalyst by adsorbing more NH3 in the selective catalytic reduction catalyst while the ammonia is prevented from being slipped from the selective catalytic reduction catalyst.

For convenience in explanation and accurate definition in the appended claims, the terms “upper”, “lower”, “inner” and “outer” are used to describe features of the exemplary embodiments with reference to the positions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teachings as well as various alternatives and modifications thereof. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 

What is claimed is:
 1. A method of controlling ammonia amount adsorbed in a selective catalytic reduction (SCR) catalyst, comprising: detecting current temperature of the SCR catalyst; reading predicted maximum temperature of the SCR catalyst after a predetermined time based on the current temperature of the SCR catalyst; determining a target adsorption amount of ammonia (NH3) based on the predicted maximum temperature of the SCR catalyst; and controlling amount of urea or the NH3 injected into exhaust gas based on the target adsorption amount of the NH3 and current adsorption amount of the NH3.
 2. The method of claim 1, wherein the target adsorption amount of the NH3 is a maximum NH3 amount that is adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.
 3. The method of claim 1, wherein the target adsorption amount of the NH3 is a value obtained by multiplying a predetermined safety factor to a maximum NH3 amount that is adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.
 4. The method of claim 1, wherein the reading of the predicted maximum temperature of the SCR catalyst after the predetermined time is performed when the current temperature of the SCR catalyst is higher than or equal to urea conversion temperature.
 5. The method of claim 1, wherein the predicted maximum temperature of the SCR catalyst after the predetermined time according to the current temperature of the SCR catalyst is stored in a predetermined map.
 6. The method of claim 5, wherein the predetermined map is stored in a non-volatile memory of a vehicle.
 7. The method of claim 5, further comprising: detecting actual maximum temperature of the SCR catalyst for the predetermined time; determining whether the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time; and storing the actual maximum temperature of the SCR catalyst for the predetermined time as the predicted maximum temperature of the SCR catalyst after the predetermined time in the predetermined map when the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time.
 8. An exhaust system comprising: an engine generating driving torque by burning mixture of air and fuel and exhausting exhaust gas generated at combustion process through an exhaust pipe; a reducing agent supplier mounted on the exhaust pipe downstream of the engine and adapted to inject urea or ammonia (NH3) into the exhaust gas, wherein the urea is decomposed into the ammonia; a selective catalytic reduction (SCR) catalyst mounted on the exhaust pipe downstream of the reducing agent supplier and adapted to absorb the ammonia and to reduce nitrogen oxide contained in the exhaust gas using adsorbed, injected or decomposed ammonia; a temperature sensor detecting temperature of the SCR catalyst; and a controller reading predicted maximum temperature of the SCR catalyst based on current temperature of the SCR catalyst after a predetermined time, determining a target adsorption amount of the ammonia based on the predicted maximum temperature of the SCR catalyst, and controlling amount of the urea or the NH3 injected from the reducing agent supplier based on the target adsorption amount of the NH3 and current adsorption amount of the NH3.
 9. The exhaust system of claim 8, wherein the target adsorption amount of the NH3 is maximum NH3 amount adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.
 10. The exhaust system of claim 8, wherein the target adsorption amount of the NH3 is a value obtained by multiplying a predetermined safety factor to a maximum NH3 amount adsorbed in the SCR catalyst at the predicted maximum temperature of the SCR catalyst.
 11. The exhaust system of claim 8, wherein the controller reads the predicted maximum temperature of the SCR catalyst after the predetermined time only when the current temperature of the SCR catalyst is higher than or equal to urea conversion temperature.
 12. The exhaust system of claim 8, wherein the predicted maximum temperature of the SCR catalyst after the predetermined time according to the current temperature of the SCR catalyst is stored in a predetermined map.
 13. The exhaust system of claim 12, wherein the predetermined map is stored in a non-volatile memory of a vehicle.
 14. The exhaust system of claim 12, wherein the controller stores an actual maximum temperature of the SCR catalyst for the predetermined time as the predicted maximum temperature of the SCR catalyst after the predetermined time in the predetermined map when the actual maximum temperature of the SCR catalyst for the predetermined time is higher than the predicted maximum temperature of the SCR catalyst after the predetermined time. 